The Health Influences of Puberty (HIP) Study is designed to explore the relationships between puberty and the onset of type 2 diabetes in adolescents. The results of this study will help us better understand how to prevent type 2 diabetes in these youth. Children go through many changes during puberty, including important hormonal and behavioral alterations. Among these changes, it has long been known that, during puberty, insulin does not work as well as it does before and after puberty. This is called physiologic insulin resistance. In healthy children, this does not cause diabetes or affect blood sugar in any way because the body is able to compensate by making more insulin. Indeed, this is thought to be an important part of the adolescent growth spurt. However, in some children with increased risk for developing type 2 diabetes due to obesity and genetics, the worsening insulin resistance of puberty cannot be compensated for and these youth get diabetes early. The investigators believe this is because type 2 diabetes is rarely, if ever, seen before puberty begins, and the peak of diabetes onset in adolescents occurs at the time of the worst insulin resistance. This specific research project has two goals: 1. To examine effects of obesity on how well the body's insulin works during puberty, and 2. To see if treatment of obese children during this critical period of puberty with a medication that improves insulin resistance (metformin) will help prevent early onset type 2 diabetes.

As measured by in intravenous glucose tolerance test (IVGTT). Patients are randomized to receive metformin or placebo at Tanner stage 2-3 of puberty. They are reassessed at Tanner 4 and again at Tanner 5. At that point, the treatment is stopped and they are reassessed 6 months after stopping treatment to see if effects of treatment persist.

After randomization, the study drug (metformin or placebo) is gradually titrated to full dose of 1000 mg BID (or to maximum tolerated, at least 500 mg BID) over a period of 4 weeks to minimize adverse gastrointestinal effects. Participants are seen every three months to measure compliance and dispense new study drug. Every 6 months, they also have a physical examination in order to determine puberty staging. Study measurements (IVGTT, bloodwork, DXA) are performed at Tanner 4 puberty and Tanner 5 (puberty completion), at which time the study drug is stopped. Study measurements will be performed again 6 months after study drug is completed to assess if effects are persistent after study drug is stopped. During the treatment period, all participants receive standard lifestyle counseling.

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Please refer to this study by its ClinicalTrials.gov identifier: NCT01775813